Table_1_Individual Sea Urchin Coelomocytes Undergo Somatic Immune Gene Diversification.DOCX

The adaptive immune response in jawed vertebrates is marked by the ability to diversify somatically specific immune receptor genes. Somatic recombination and hypermutation of gene segments are used to generate extensive repertoires of T and B cell receptors. In contrast, jawless vertebrates utilize a distinct diversification system based on copy choice to assemble their variable lymphocyte receptors. To date, very little evidence for somatic immune gene diversification has been reported in invertebrate species. Here we show that the SpTransformer (SpTrf ; formerly Sp185/333) immune effector gene family members from individual coelomocytes from purple sea urchins undergo somatic diversification by means of gene deletions, duplications, and acquisitions of single nucleotide polymorphisms. While sperm cells from an individual sea urchin have identical SpTrf gene repertoires, single cells from two distinct coelomocyte subpopulations from the same sea urchin exhibit significant variation in the SpTrf gene repertoires. Moreover, the highly diverse gene sequences derived from single coelomocytes are all in-frame, suggesting that an unknown mechanism(s) driving these somatic changes involve stringent selection or correction processes for expression of productive SpTrf transcripts. Together, our findings infer somatic immune gene diversification strategy in an invertebrate.

有颌脊椎动物的适应性免疫应答，以对特异性免疫受体基因进行体细胞多样化修饰为核心特征。通过体细胞重组与基因片段高突变，可产生大量多样性的T细胞受体（T cell receptor, TCR）与B细胞受体（B cell receptor, BCR）库。与之相对，无颌脊椎动物则采用一套基于拷贝选择的独特多样化系统，组装其可变淋巴细胞受体（variable lymphocyte receptors, VLR）。迄今为止，尚未见无脊椎动物物种中存在体细胞免疫基因多样化的有效报道。本研究显示，紫海胆单个体腔细胞中的SpTransformer（SpTrf；原名为Sp185/333）免疫效应基因家族成员，可通过基因缺失、基因重复以及单核苷酸多态性（single nucleotide polymorphism, SNP）的获得发生体细胞多样化修饰。尽管同一只海胆的精子细胞拥有完全一致的SpTrf基因库，但来自同一只海胆的两个不同体腔细胞亚群的单个细胞，其SpTrf基因库却存在显著差异。此外，从单个体腔细胞中获取的高度多样化基因序列均保持读框完整，这表明驱动这些体细胞变化的未知机制，包含了针对功能性SpTrf转录本表达的严格选择或校正过程。综上，本研究结果揭示了无脊椎动物体内存在体细胞免疫基因多样化的策略。